Corner joint between two timber beams



M y 7, 1968 E. ANTTILA 3,381,985

CORNER JOINT BETWEEN TWO TIMBER BEAMS Filed Jan. 18, 1965 2 s s 1 May'7,1968 E. ANTTILA CORNER JOINT BETWEEN TWO TIMBER BEAMS Filed Jan. 18,1965 2 Sheets-Sheet f:

United States Patent 3,381,985 CORNER JOINT BETWEEN TWO TIMBER BEAMSErkki Anttila, Isokaari 32C, Helsinki 20, Finland Filed Jan. 18, 1966,Ser. No. 521,367 4 Claims. (Cl. 287-2092) ABSTRACT OF THE DISCLOSURE Acorner joint between two timber beams formed by a plurality ofadhesively secured layers, each of which includes a plywood panelextending longitudinally in one of the beams, and a plank extending inthe lengthwise direction of the other beam and secured to the marginaledge of a panel of an adjacent layer along the outer edge of the cornerjoint.

This invention relates to a corner joint between two timber beams whichare perpendicular to each other and constituted by layers runningparallel to the plane of each beam, the layers overlapping one anothernear the corner joint in such a way that one layer of one beam isadjoined by one layer of the other beam and both layers are joined toeach other by glueing.

Similar corner joints are used, for example, in structural frames suchas triple-joint or double-joint frames. A horizontal beam carries theweight of a roof which gives rise to bending stresses in the cornerjoint which in turn are converted into shearing forces inside the joint.

Panels, planks or the like have in the past been used for the productionof such joints as these. Due to the shearing forces inside the cornerjoint, the joint itself has had to be made particularly solid betweentwo beams. Since the shearing forces act parallel to the plane of thejoints, i.e. the wood used to make the corner joint has a tendency tosplit, it is clear that joints such as these are unable to withstandintensive stressing because their shear strength in the direction of theconstituent fibres of the wood is extremely low. For this reason, framesmanufactured with the aid of these joints have a limited free span.

An object of the present invention is to obviate these disadvantages andto provide a corner joint which is able to withstand the same loads asthe known joints, but which at the same time makes possible a muchlighter construction. On the other hand, it is possible by means of thecorner joint according to the invention to manufacture structural frameswith a considerable free span without any need for the frame to beexcessively solid. The invention is characterized by the fact that thelayers of the beams near the joint are constituted at least in part of aplywood panel of which, the fibres of the outer surface ply or veneerrun in substantially the same direction as the beam with which theplywood panel is associated. Additionally a longitudinal plank extendsfrom each panel in the lengthwise direction of the other beam. Theadvantage of the corner joint according to the invention over the knowncorner joints is primarily that the shear strength of the plywood isabout six times as high as the shear strength of the constituent wood inthe direction of the fibres, as proven by tests. By virtue of the factthat the fibres of the surface veneer of the plyood panel run insubstantially the same direction as the beam to which the plywood panelis associated, each layer has the same modulus of elasticity near thecorner joint, as a result of which the strength of each layer is fullyutilized.

According to one preferred embodiment of the invention, the plank ispositively relative to its associated panel to lie along a longitudinalmarginal edge of the panel of the adjacent layer, at the outer edge ofthe corner joint.

As a result, the strength of the corner joint is further in- "icecreased because the planks rest on those edges of the corner jointsubject to tensile stresses and because as already known the tensilestrength of wood in "the direction of its constituent fibers isrelatively high.

The accompanying drawings, show one embodiment of the invention wherein:

FIGURE 1 is an elevation view of a triple-joint frame,

FIGURE la shows a moment distribution on such a frame,

FIGURES 2 to 5 are each side elevations of the various plywood layers ofthe corner joint of a triple-joint frame,

FIGURE 6 is a section through the corner joint taken on the line VI-VIof FIGURE 1,

FIGURE 7 is a section through the corner joint taken on the lineVII--VII of FIGURE 1,

FIGURE 8 is a sectional view taken on the line VIII-VIII of FIGURE 6,

FIGURE 9 is a sectional view taken on the line IXIX of FIGURE 7,

FIGURE 10 is a sectional view taken on the line XX-XX of FIGURE 7.

In the drawing, the reference 1 denotes a substantially vertical beamand the reference 2 a substantially horizontal beam. The beams 1 and 2are joined together by means of the corner joint according to theinvention. The structure of this corner joint can be best explained withreference to the method by which it is assembled. The plywood section 3together with two planks 4 and 5 are arranged in a glue press in therelative positions shown in FIGURE 2. The next layer to be appliedconsists of two planks 6 and 7 and a plywood section '8. The next orthird layer is constituted by a plywood section 9 and two planks 10 and11 forming part of beam 1, and two planks 12 and 13 which, as shown inFIGURE 4, project into the substantially horizontal beam 2. Two planks14 and 15 together with a plywood panel 16 are then applied as thefourth or middle layer, as shown in FIG- URE 5. Since the corner jointis symmetrical on the center plane of the beams 1 and 2, another layeris applied to the center layer as shown in FIGURE 4, which in turnreceives another layer as shown in FIGURE 3 and finally yet anotherlayer as shown in FIGURE 2. The surface of the top layer, the bottom ofthe final layer and both faces of all the other layers are coated withglue before being fitted together. The assembly thus formed is thensubjected to compression alone or together with other similar assembliesplaced one above the other. When the glue has hardened, the corner jointbetween one substantially vertical and one substantially horizontal beamis complete.

In this embodiment, the corner joint consists mainly of the entire,substantially vertical beam 1 and of part of the substantiallyhorizontal beam 2. To facilitate transport, the other part of thehorizontal beam is fitted at the assembly site. The continuation of thehorizontal beam 2 is arranged near the neutral point of the bendingstresses. This is evident from FIG. 1a wherein there is shown thedistribution of the moments on the frame. As shown in FIG. la themaximum moment is applied at the corner joint of the frame.

Another advantage of the corner joint of the invention over known cornerjoints is that it is simple and therefore inexpensive to manufacture.

Corner joints according to the invention may be made several at a timeeither at the factory or at the assembly site, whereas the known typesof corner joint can only be produced singly at the assembly site bynailing them together.

The various embodiments of the invention may be significantly modified,in particular as regards the number of layers in the corner joint. Ifthe frame is to have a considerable free span, several layers will ofcourse be needed for the corner joint.

The invention is not limited to a specific material in the remainingparts of the beams. In the embodiment illustrated, the other part of thehorizontal beam merely consists partly of wood and partly of plywood,although it can consist entirely of wood or entirely of plywood.

What I claim is:

1. A laminated corner joint between two timber beams which aresubstantially perpendicular to each other and lie in a common plane,said joint comprising a plurality of layers extending parallel to theplane of the beams, the layers of each beam being overlapped andadhesively secured in succession adjacent the corner between the twobeams, at least one layer of each beam being constituted at least inpart of a plywood panel having grain running in the same direction asthe associated beam and an elongated plank secured along an end edge ofthe plywood panel and continuing into the corresponding layer of theother beam along its longitudinal edge.

2. A corner joint as claimed in claim 1 wherein said planks arerelatively positioned with respect to the plywood panels of said layersto be disposed at the longitudinal outer marginal edges of the plywoodpanels of adjacent layers.

3. A corner joint as claimed in claim 1 wherein one of said layersincludes longitudinal planks which extend from the associated plywoodpanel in the lengthwise direction of both beams.

4. A corner joint as claimed in claim 1 wherein at least one other layerof each beam is constituted by a plywood panel coextensive with one beamand having elongated planks secured to said latter plywood panel edge inend abutted relation and extending into the corresponding layer of theother beam.

References Cited FOREIGN PATENTS 624,875 6/1949 Great Britain.

CARL W. TOMLIN, Primary Examiner.

WAYNE L. SHE/DD, Assistant Examiner.

